This study will examine multiple cause mortality differentials among various demographically defined components of the U.S. population and the patterns of change or stability in these differentials for the years 1969, 1972, and 1975. Preliminary evidence suggests that overall mortality has declined rather sharply during these years following a period of relative stability that began in the early 1950's. In order to effectively study mortality trends, it is necessary to have a firm grasp of the issues surrounding the certification and vital registration system that generate these data and of the assumptions about disease models made in the different methods of analyzing mortality data. Medical studies of specific diseases based on original death certificates indicate the desirability of more fully utilizing information on all the conditions and causes of death listed on the certificate. This is due to the difficulty in representing the complexity of medical facts by a single underlying cause of death, especially when chronic illness or a combination of chronic illnesses or a combination of chronic and acute illnesses are implicated in an individual's death. Thus, if national mortality statistics are to be generally useful in describing disease-specific mortality under conditions in which the age structure has shifted to greater proportions of elderly, and the disease structure towards an increase in the prevalence of chronic diseases, it is necessary to explicity study multiple cause mortality statistics. Until now, research of this type has seldom been conducted for the entire U.S. population because of a lack of such data for individuals and an associated lack of conceptual and methodological development of multiple cause of death models. we intend to develop guidelines for the appropriate applications of multiple cause of death data and to evaluate several methodologies for its analysis. The methodological efforts are directed in particular to issues related to various assumptions about the independence or dependence of diseases causing death. The timeliness of the study is underscored by the National Center for Health Statistics' recent decision to release multiple cause of death data for individuals.